Glass sealants are used, in part, in making electronic parts such as semiconductor devices and fluorescent character display tubes. For example, U.S. Pat. No. 5,145,803 (Daimer et al.) reports a glass sealant comprising a lead borate glass used in the fabrication of integrated circuits. U.S. Pat. No. 4,883,777 (Yamanaka) reports a lead-containing glass sealant for the manufacture of semiconductors and other electronic devices. U.S. Pat. No. 4,058,387 (Nofziger) and U.S. Pat. No. 4,120,678 (Francel et al.) report a glass sealant used to seal a glass faceplate to a glass funnel of a cathode-ray tube. Glass sealants form a bond between two substrates when heated and when used on electronic devices are preferably made of low-softening point glass to avoid damage to the article being sealed. Some low-softening point glass sealants melt and flow at a temperature below 500.degree. C., and most frequently between 400.degree. C. and 475.degree. C.
Most glass sealants are pastes applied by extrusion so that a continuous amount of paste is placed between two surfaces to be sealed. The fluid nature of the paste makes the application of a very thin and uniform layer of paste free of voids difficult to achieve. Gaps of paste, or uneven paste thickness along the surfaces to be sealed may result in poor substrate bonding. Excess paste, upon heating and cooling of the paste, may result in debris particles being formed external to the region being sealed. These debris particles may come loose and damage the internal components of the article being manufactured.
Pastes are soft, smooth, and thick mixtures that when used are messy. Pastes are easily transferred to other parts of the articles being manufactured, to technicians operating equipment, to equipment used in the manufacturing process, and to other work areas. Pastes may accidentally be applied to clothing or to skin creating a potential safety hazard depending upon the composition of the pastes. Furthermore, pastes may contain volatile solvents which emit unpleasant and possibly hazardous odors. Pastes may also have a short shelf life since the volatile solvent in the paste may evaporate leaving a dried material which cannot be applied to a substrate. As a result of this, often times a large percentage of paste is discarded as waste.
In addition to the foregoing, pastes may contain lead which is hazardous to workers when the lead-containing paste contacts skin or is ingested. Lead containing glass sealants must be disposed of properly to avoid environmental issues. Additional clean-up time may be necessary to remove unwanted paste.